Electric transducer system



Dec. 7, 1954 K. s. LloN ErAL ELECTRIC TRANSDUCER SYSTEM Filed Oct. 20. 1949 9 Sheets-Sheet l File'd Oct. 20, 1949 Dec- 7, 1954 K. s. LION ETAL 2,696,556

ELECTRIC TRANSDUCER SYSTEM 9 ASheets--Sheet 2 .Jo/m W. Sheefz 3rd by M a-l m Attorneys Dec. 7, 1954 K. s. LloN Erm. 2,696,566

ELECTRIC TRANSDUCER SYSTEM Filed Oct. 20. 1949 9 Sheets-Sheet 3 l ll/ l0? F ly. /6

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- /55 M7 #//5/ /25 :Ik/53 9?/ f4 /2/ l /29 /7 9i l l las?l C, M C- 2 Fl' /nvenors g2g Kuril $.L/'on John W Sheer: 3rd bym M 1&4

A tfomeys Dec. 7, 1954 K. s. LvloN ETAL. 2,696,566

ELECTRIC TRANSDUCER SYSTEM Filed Oct. 20, 19.49 9 Sheets-Sheet 4 C /59 I LZ f4 /6/ RF Osci//ara- Recs/ver 3:@1

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Inventors Kurt `S`../'on Jahn W. Sheefz 3rd @Vzw am# m Attorneys Dec. 7, 1954 K. s. LION m-AL 2,696,566

ELECTRIC TRANsDucr-:R SYSTEM Filed oct. 2o. 1949 9 sheets-sheet 5 RUDDER E L EVA TONS A/L ERONS *M* r"-\L Moor Mofor Moor I I I I I I Control Confro/ Control Amplifier 4 Amplifier Amp//f/er I l I I ,231 lgs /22/ //25 /59` m) 45 f /n venfors Attorneys Dec. 7, 1954 K. s'. LION HAL 2,696,566

ELECTRIC TRANSDUCER SYSTEM Filed Oct. 20. 1949 9 Shee'ts-Sheet 7 /n venfors Kurt S. L ion lo/m, n. Sheefz 3rd by W Aameys Dec. 7, 1954 K. s. LION ETAL ELECTRIC TRANSDUCEIR SYSTEM 9 Sheets-Sheet 8 Filed 0012. 20. 1949 Y2 I Fly. 40.

/n ven/ors Kurt 5. L/'on ./o/m w sneek' 3rd by mw 7am Attorneys Dec. 7, 1954 K. s. LION ETAL 2,696,566

ELECTRIC TRANSDUCER SYSTEM Filed Oct. 20. 1949 9 Sheets-Sheet 9 247 J /nvenfors Kurt S. L/'on l .47. F g John W Shea/z .3rd

Attorneys United States Patent Ofice Patented Dec. '7, 1954 ELECTRic TRANSDUCER SYSTEM Kurt S. Lion, Watertown, Mass., and .lohn W. Slieetz 3rd, Fairlington, Va.

Appiication october 2o, 1949, serial No. 125,322

31 Claims. (ci. 307-52) The present invention relates to electric circuits and more particularly to circuits employing discharge tubes. This application is a continuation-in-part of our copending application Serial No. 30,546, filed on June 2, 1948.

ln the said eopending application, it was disclosed that if an ionizable medium, such as a gas-filled tube, having two internal electrodes is inserted in an alternatingcurrent field of sufiicient intensity to produce an ionized discharge within the medium, such as, for example, in a sufiiciently intense radio-frequency field, a direct-current voltage will be developed between the two electrodes even though there is no source of energy connected therebetween. The polarity and magnitude of this directcurrent voltage is determined by the field distribution surrounding the tube. Regions of operation are described where variations in the field distribution produce substantially linear corresponding variations in directcurrent voltage, as Well as variations obeying other laws. Mechanical and electrical systems for varying the field distribution in accordance with a predetermined signal are also described, and some of these are reproduced here for completeness.

y An object of the present invention is to provide new and improved circuits for producing these direct-current voltages from alternating electric fields.

Another object is to provide novel circuits for converting or transducing mechanical vibrations, forces or other motions into corresponding electrical voltages.

A further object of the present invention is to provide circuits of the character described adapted to operate in conjunction with a wide variety of control circuits.

Other and further objects will be explained hereinafter and will be more particularly pointed out in the appended claims.

In summary, the present invention is directed to novel electric systems of the type having, in combination,

means comprising an ionizable medium, preferably a gaseous medium, provided with two electrodes between which potential gradients may be established to ionize the medium and an output circuit connected between the electrodes whereby a voltage may be produced in the output circuit in response to the ionization of the medium without the aid of a source of energy therein. Preferred constructions and circuits as Well as preferred potentialgradient producing electric fields are treated in detail.

the use of such systems as transducers under the control of a wide variety of signal-producing means or forces is hereinafter discussed, applications to servo-mechanism systems, gyroscope systems, telemetering and other measurement systems, as well as to other types of systems being particularly pointed out.

The invention will now be described in connection with the accompanying drawings, Fig. l of which illustrates a basic circuit diagram of an apparatus constructed in accordance with the invention described in the said co-pending application; Fig. 2 is an experimental plot of the sensitivity of the apparatus of Fig. l; Fig. 3 is a modified apparatus for producing results similar to those obtained with the apparatus of Fig. l; Figs. 4 and 5 are similar circuit diagrams of apparatus operated with modulated high-frequency fields in accordance with one of the novel features of the present invention, the apparatus of Fig. 5 being shown connected to a balanced amplifying system; Fig. 6 is a modification of the apparatus of Fig. l responsive to motions or movements produced in accordance with a predetermined law; Fig. 7 is a similar apparatus constructed in accordance with a preferred form; Fig. 8 illustrates experimentally obtained sensitivity curves of the apparatus of Fig. 7; Figs. 9 and 10 are circuit diagrams of modifications of the circuit of Fig. 7; Fig. ll is a further modification employing a resonant output circuit and illustrating another feature of the present invention; Fig. l2 is an experimentally obtained curve illustrating the operation of the circuit of Fig. 1l; Figs. 13 to l6 are further modifications of the apparatus of Fig. 7, Figs. 14 and l5 employing external ring electrodes; Figs. 17 to 19 are moditications of the circuit of Fig. 9, respectively illustrating movement in fields produced by wire electrodes, electrodes shaped in accordance with a predetermined law, and twodimensional electrode arrangements; Fig. 20 illustrates a modified circuit employing a plurality of transducer elements arranged to produce voltages representative of the sum of or the difference between two mechanical displacements or other movements in accordance with a further feature of the present invention; Figs. 21 and 22 are modifications illustrating, respectively, parallel and series-connected apparatus adapted to indicate the sum of or the difference between two or more mechanical displacements or other movements; Figs. 23 and 24 are schematic diagrams illustrating the application of the apparatus of rigs. or '7, or the various modifications thereof, as amplitude, frequency or phase modulators of a radio-frequency transmitter; Fig. 25 illustrates the apparatus of Fig. 7 under the control of an electrically varying temperature indicator; Fig. 26 shows the control of the apparatus of Fig. l by a mechanically varying temperature indicator; Fig. 27 is a schematic diagram of the apparatus of Fig. 7 controlled by a wind-velocity or pressure indicator; Fig. 28 is a similar diagram illustrating control by a clock, meter, counter, indicator or similar device; Fig. 29 illustrates the control of the circuits ot' the present invention by an angular accelerometer; Fig. 30 illustrates control effected in accordance with the proximity of external objects; Fig. 3l is a diagram of a plurality of transducers constructed in accordance with the present invention and controlled by various moving portions of a vehicle, such as an aircraft or projectile; Fig. 32 shows the operation of the present invention as an amplifier of small voltages that are caused to eect mechanical displacements; Fig. 33 illustrates the apparatus of Fig. l adapted to indicate the size of objects carried upon a conveyor belt; Figs. 34 and 35 respectively illustrate apparatus of the type shown in Figs. l and 7, or the various modifications thereof, under the control of a servo-mechanism system; Figs. 36 and 37 are schematic diagrams of servo-mechanism systems embodying control and follow transducers; Fig. 38 illustrates the apparatus of Fig. 19 under the control of twodimensional servo-mechanisms; Fig. 39 shows the preferred apparatus of Fig. 5 employed with thyratron control tubes; Figs. 40 and 4l illustrate the apparatus of Fig. 7 under the control of a gyroscope; Figs. 42 and 43 respectively illustrate gyroscopic control of the basic circuits of Figs. l and 3; Fig. 44 is a schematic diagram of a circuit similar to Fig. 7 under the control of a temperature indicator of the type shown in Fig. 26 cooperative with heating and cooling units for providing constant temperature; Fig. is a modified apparatus in which a bellows is provided to permit the movement of one of the principal electrodes of the apparatus of Fig. l, or of the various other embodiments; Fig. 46 shows a phonograph pick-up or other surface-measuring device controlling the apparatus of Fig. 7; and Fig. 47 illustrates a further modification of the circuit of Fig. 7 controleld by a strain gauge or accelerometer.

A gas-discharge tube is illustrated in Fig. l as provided with two principal preferably internal electrodes 3 and 5 spaced from one another in an envelope 1. The envelope 1 is preferably constituted of glass or similar electric-wave permeable material, though metal and other conducting envelopes may be employed under some circumstances, as will later be discussed. The principal electrodes 3 and 5 are shown as plane metal discs, but any electrode configuration, including thin wires, as shown in Figs. 17 to 19, 28 and 42, may be used.

The envelope 1 may be filled with any desired ionizable dielectric medium such as any well-known ionizable solid or, preferably, a gas under low, medium or high pressure. While helium and neon gas have been found to be particularly well-suited to the purposes of the present invention, any other gaseous media such as air, hydrogen, argon, krypton, mercury vapor, to mentionv but a few, may also be employed. The medium may, if desired, be sealed under pressure within the envelope 1, or it may be continuously maintained under pressure by means of a conventional vacuum system, not shown.

A third electrode 9, preferablyv in the form of a ring or band external to and surrounding the envelope 1, is shown movable from a center position O toward either end of the envelope 1.

An alternating or pulsating voltage hereinafter referred to as alternating-current, oscillator 17 may be connected between the third or movable electrode 9 and the electrode 3, which may, if desired, be grounded, as shown. The oscillator or generator 17 is preferably a radio-frequency signal generator, though lower-frequencied oscillators of, for example, audio, ultasonic and Video frequencies may be employed. The electrodes 3 and S are coupled at the radio or other alternating frequency of the oscillator 17 by the condenser C. An output circuit comprising conductors 2 and 4 is connected between the electrodes 3 and S, and no source of energy such as a batteryfor other device is required in the output circuit. An indicator such as a meter M, shown dotted, may be directly connected across the output circuit 2 4. As explained in the said copending application, providingv .the peak voltage of the alternating potential impressed between the electrodes 3 and 5 produces a field sufficient to cause the gas or other medium in the tube 1 to ionize, a direct-current potential V will be produced between the electrodes 3 and 5 in the output circuit 2 4, in accordance with the phenomenon relied upon in the present invention, even though no battery orother source of energy is connected in thev output circuit. A much smaller voltage is required to ionize a gas at radio frequencies than at lower frequencies so that the radio-frequency spectrum is particularly useful for this and for other reasons. At radiofrequencies, furthermore, relatively high-pressure gases, such as the before-mentioned helium and neon are preferable.

As the electrode -9 is moved closer to the electrode 3 than to the electrode 5, downward from the center position O in Fig. 1, the-direct-current output voltage V will have the polarity shown in Fig. l. When, on the other hand, the electrode 9 is moved closer to the electrode 5, upward from the center positionO in Fig. l, the reverse polarity will obtain in the output circuit 2-4. The magnitude of the voltage V, furthermore, within limits that will later be discussed, increases as the electrode 9 is moved closer to one or the other of vthe principal electrodes 3 or 5.

Fig. 2 is a reproduction ofa characteristic curve that we have experimentally obtained with an air-illed tube similar to that shown in Fig. l, operated under a pressure of 0.87 millimeters of mercury. The oscillator 17 was operated at a frequency of 23.2 megacycles with a root-mean-square (R. M. S.) amplitude of 100 volts, and was connected between the movable electrode 9 and the grounded electrode 3, as illustrated in Fig. l. The capacitor C had a value of about 0.01 microfarad so that both of the principal electrodes 3 and 5 vmight be at ground potential with respect to the radio-frequency current of the oscillator 17, but only the electrode 3 `would be at direct-current ground potential. The spacing between the principal electrodes 3 and 5 was about 60 millimeters. In Fig. 2, the direct-current voltage V obtained between the output terminals 2 and 4 is plotted along the ordinate as a 4function of the position of the movable electrode 9 from the center position O, shown at the 30 millimeter mark along the abscissa. When the electrode 9 was positioned exactly at the center position O, half-way between the principal electrodes 3 and 5, equal length, cone-shaped, elongated glow discharges were observed in the tube 1, glowing from a virtual electrode within the tube 1, corresponding to the electrode 9, towards each of the principal electrodes. For this condition, zero output voltage was measured in the output circuit between the terminals 2 and 4. Since the alternating field produced potential gradients between the electrode 9 and each of the principal electrodes 3 and 5 of equal magnitude and opposite polarity, a cancellation of current ow in the ionized gas was produced. As the electrode 9 was moved closer to the electrode 3, the glow discharge between the electrode 9 and the electrode 3 became of shorter length and more intense, while the glow discharge between the movable electrode 9 and the electrode 5 became longer and less intense. This potential gradient differential resulted because the impedance between the electrode 9, or its virtual electrode inside the tube 1, and the electrode 3 became less than the impedance between the electrode 9 and the other principal electrode 5. Since the potential gradients, therefore, between the electrode 9 and the electrode 3 became greater than the potential gradients between the electrode 9 and the electrode 5, a resultant current ow in the direction from the electrode 3 towards the electrode 5 was produced and a positive direct-current voltage V resulted between the terminals 2 and 4 in the output circuit. The magnitude of the voltage V increased positively as the electrode 9 approached. the principal electrode 3. When, for example, the separation of the electrode 9 from the principal electrode 3 was 21 millimeters, a voltage V of 2O volts was produced; when the separation was .13 millimeters, 40 volts resulted', and for a separation of about 5 millimeters, a maximum positive voltage Vmax of 6() volts was produced, as shown at point A in Fig.. 2.

By moving the electrode 9 from the center position O of the tube 1 towards they other principal electrode 5, the increased potential. gradients between the Velectrode 9 and the electrode 5 became greater than the potential gradients betweenthe electrode 9 andthe principal electrode `3, producing a resultant current ow from the electrode 5 towards the electrode 3. A negative voltage V, therefore, resulted in the output .circuit 2 4. `Because of the vapproximate symmetry of the principal electrodes and of the tube structure, the magnitude `of the negative voltage Vas a function of the displacement of the electrode 9 from the center position O toward the principal electrode 5 was found to vary substantially in the same manner as the magnitude of the positive voltage V for the corresponding kdisplacements of the electrode 9 from the center position O toward the principal electrode 3. Had the two electrode structures or the tube construction been unsymmetrical, however, different variations would have been produced. A maximum negative voltage Vmax of 60 Volts was obtained when the electrode 9 was at a position 52.5 mm. from the electrode 13, orzabout 6.5 mm. from the electrode 5, as shown in A substantially linear variation of direct-current output voltage V from positive to negative values within limits of the adjustment of the electrode 9 from a position separated about 5 mm. from the principal electrode 3 to a position lseparated about 6.5 mm. from the other principal .electrode ,5, was produced in .this particular tube. The sensitivity of the tube 1 in ,this operating region may be expressed in terms of the voltage V per millimeter of Vlateral movement or displacement of the electrode 9. The sensitivity of this particular tube was found to be about 2.5 volts per millimeter of displacement. If sign be disregarded, the tube sensitivity iS about 5.0 volts per millimeter of displacement of the electrode 9. A very sensitive linear-position indicator or ultra-micrometer is thus provided. If, for example, a dimension of an article is to be measured to ahighdegree of accuracy, a scale would be of little value. If one end of the article is placed at a'position adjacent one of the principalelectrodes, for example, and the ring electrode 9 is moved to the other end of the article, however, .the output voltage V will accurately measure the dimension of the article or variations in this dimension, as `more fully discussed in the said copending application.

If the electrode 9 is moved from the center of the tube 1 continuously closer to one of the `principal electrodes, therefore, a linear direct-current Voltage increase is produced as the system transduces each unit of movement into voltage. Movement towardsfone principal electrode produces an increasing .positive voltage, and movement towards the other electrode an increasing negative voltage. A point is reached, however, when, upon slight further movement of the electrode 9 'towards the closer principal electrode, the longer and weaker gas ldischarge between the electrode 9 and the y'further `principal electrode suddenly breaks away from the surface of the 'further principal electrode, and a sharp decrease in ymagnitude of the direct-current output voltage V is produced. The points where this sharp inversion takes place are designated at A and B in 2.

For the air-filled tube previously described, for example, point A was found to occur when the electrode 9 was about 5.0 millimeters from the principal electrode 3, and

i point B occurred when the electrode 9 was about 6.5

millimeters from the principal electrode 5. Movement of the electrode 9 just one millimeter closer to the electrode 3 from the point A produced a sudden voltage decrease of about volts, while similar movement from the point B towards the electrode 5 produced a sharp 3lvolt decrease. Further movement of the electrode 9 towards the closer principal electrode produced smaller and smaller output voltages. Some tubes that were tested displayed other minor points of voltage inversion in the region between, for example, the point A and the electrode 3, where further relatively narrow regions of voltage increase and decrease were obtained.

While the whole region A B may be used for producing linear voltage variations corresponding to displacements of the electrode 9, the center of the tube may be used as a zero reference on opposite sides of which positive increasing and negative increasing voltages V may be produced. The circuits embodying the present 0f invention, of course, need not be operated about a zero output voltage reference value, but may be operated at any desired reference value. lf, for example, the electrode 9 is vibrated back and forth, preferably about the center of the tube 1, by any vibrating means, such as, for 1 example, those later discussed in connection with Figs. 32 and 47, an alternating voltage may be produced in the output circuit 2 4 of peak magnitude linearly related to the vibrational displacement of the electrode 9. The frequency of periodicity of the polarity reversals of `the output voltage bears no relation to the frequency or periodicity of the input voltage from the oscillator or generator 17, but is determined by the frequency of vibration of the electrode 9. The ring 9, as a further example, has been mounted on the cone of a loud speaker driven by an audio oscillator, not shown, and alternating voltages up to over 20,000 cycles were successfully produced.

Substantially linear operation over a somewhat more limited region may also be obtained, of course, on the very steep portion of the characteristic curve just to the left of the point A, or to the right of the point lB, illustrated in Fig. 2.

If it is desired to operate the system with a fixed direct-current voltage output or with the electrode 9 at a predetermined position, and to indicate a variation from either of these conditions, the points A and B may be conveniently employed as operating points. Slight movement of the electrode 9 in either direction from the points A and B will sharply and markedly decrease the magnitude of the voltage V. The points A and B may easily be located again7 furthermore, by peaking the voltage output. Since the slope of the voltage curve to the left of the point A or to the right of the point B has been found customarily to be steeper than the slope of the linear portion A B, as shown in Fig. 2, the relative voltage changes per unit movement of the electrode 9 may indicate in which direction the electrode has moved from the point A or B.

We have found that, if, in a given tube, the pressure of the gas is increased, the slope of the linear portion A B will, in general, increase also, producing greater tube sensitivity. The increase in pressure, however, usually decreases the value of the maximum output voltage Vmax at points A and B, and decreases the length of the region of the tube over which the linear characteristic A B occurs.

As an illustration, for one particular experimental tube, a variation of tube sensitivity or slope of the characteristic curve with pressure of the gas within the tube was measured between 0.86 millimeters of mercury pressure to 2.2 millimeters pressure. sitivity increased from 1.08 volts per millimeter deection of the movable electrode 9 to 1.59 volts per millimeter deflection, and the increase was substantially linear. If, therefore, movements of the electrode 9 do not produce large enough direct-current voltages in the output circuit 2 4, the pressure of the gas in the tube 1 may be changed to increase the tube sensitivity.

It should be understood that the same phenomenon previously described, may be produced by keeping thev Within this range, the tube senv electrode 9 fixed and by varying the potential gradiets between the electrode 9 and the principal electrodes by other means. One or both of the principal electrodes may, for example, be inserted into the envelope 1 through well-known airtight bellows, as discussed in the said copending application, so that either or both of the principal electrodes themselves may be moved relative to the electrode 9. In Fig. 45, for example, the principal electrode 3 is shown movable in a conventional preferably gas-tight bellows 11 that is sealed to one end of the tube 1. With such a construction, the electrode 9 may be insetred within the envelope 1, and, indeed, the envelope 1 may be made of conducting material to shield the system from stray fields. The circuit of Fig. 45 is slightly different than, though fully equivalent to, that of Fig. l, in that the generator 17 is shown connected to the principal electrodes 3 and 5 through the respective coupling condensers C1 and C2.

The present invention is not, however, limited to the transducing of linear movements into corresponding voltages. In Fig. 3, for example, the tube 1 is shown bent along an arc, and the electrode 9 is xed to a conducting arm 15 so as to be movable along the arc of the tube 1 about a pivot 13. The oscillator 17 is connected on one side to the principal electrode 3 and on the other side through the pivot 13 and arm 15 to the ring electrode 9. The principal electrodes 3 and 5 are coupled by the condenser C in the same manner as discussed in connection with Fig. l. Angular movements of the arm 15 and its associated ring electrode 9 as indicated upon a scale 19, for example, are thus converted into corersponding directcurrent voltages in the output circuit 2 4. lf the tube 1 is operated over its linear characteristic, moreover, angular movements will be transduced into proportional directcurrent voltages.

While only linear and angular movements have thus far been discussed, it is to be understood that any kind of movements, describing any function or law, may be employed. In Fig. 6, as a further illustration, a cam 23, cut according to any desired law, is shown rotatable about a shaft 21. The rotation of the cam 23 may be indicated on an angular scale 19. As the cam 23 rotates, it displaces a lever 25 that is pivoted at one end about a pivot 27 and that carries the ring electrode 9 at the other end. By making the ring electrode 9 of sufficiently large diameter, it will not bind the tube 1 as it is displaced by the movement of the lever 25 in response to the action of the cam 23. The tube 1 may, indeed, be curved as previously discussed in connection with the system of Fig. 3. If the lever 25 is constituted of conducting material, it is preferably grounded at the pivot 27 as shown. The output voltage between the terminals 2 and 4 will thus vary in accordance with the function or law to which the cam 23 is cut. The circuit connections of the oscillator 17 to the tube electrodes are the same as those before discussed in connection with Fig. 45.

No matter what type of motions are employed with the transducer of the present invention, therefore, corresponding d1rect-current voltages may be produced without the aid of a source of energy, such as a battery, in the output circuit. Often it is desirable to amplify these directcurrent output voltages. Conventional direct-current amplifiers may be employed, but they are attendant with drift and instability. In accordance with an important feature of the present invention, by modulating the radiofrequency or other oscillator 17, stable alternating-current amplifiers may be used as will now be discussed.

in Fig. 4, as an illustration, the oscillator 17 is shown modulated with a relatively low-frequency envelope 29. The modulation voltage signals may be of any desired type such as sine-waves, complex waves, pulses, and the like. If, as hereinafter discussed, the tube is operated over certain voltage and pressure ranges, it is substantially independent of both the frequency and the magnitude of the radio-frequency voltage of the oscillator 17. The modulation 29 will then not appear in the output circuit 2 4. Only a direct-current voltage representative of the amount of displacement of the center electrode 9 will result. If, on the other hand, the tube 1 is operated over other ranges, later described, where an increase in applied voltage produces an increase in output voltage, the modulation envelope 29 will be reproduced in the output circuit 2 4 as illustrated at 3]. This output voltage 31 may be considered as a superposition of a direct-current voltage dependent upon the l .F.:cpdsition"offthe'fringr electrodef9 and aiin'ewz alternatingffcurrent' 'voltagesthatze depends? upon .thevrnodulating :voltreage. r The'polarity loff the voltage'zimpulses:dependsupon 27 the' ."polartyf fof'v the direct-,crrent voltagelrfcomponent -w'which, finf turn, i is'lidepende-,ntl upon :thel'dire'c'tiorioff-fdis- 4-nplacement ofi the ringl electrode 9'1fr0m -itscenter1po`sition. 1 l'Thefoutput ivoltage' Slrnaythus beiv ampliedn stable ii.alternating-current '.arnpliiiers, obvia'tingthefneed'fforf the #more unreliable'\directLcurrentlampliiers. The-'pulsating n @voltage '31rmay, Jon 1the'fothe. handfif Tdesired; bewap-l v plied :directly to' a direct-current'meter'for measurement e fof the ldirectcurrentf level.

A practicalfamplifyingcircuitlisshowrnin *FigL- 5','eon f; nected tothe outputflterrninals 2$4 offltheitube'" lfthat i V'is .shown connected to 'at:modulatedradio-frequencyfoscil- .-wlator "17: .in' the rmannerdiscussed-'in conneotionlwith Figs. 6': '.and.45. 1 Withthe'.. ring electrode-i9 .in-its1"ce'ntr`al position between thel principal:ele't-tlrodes'` 3;l and" 5," no -routput'voltageresults inf'rthe' outputcircuit. ^`-`When the .ring f. electrode'` is displaced," Lforf."exarnpleg-4 closerto i Athe lrprin'cipal electrode i :than ."to the prineipal electrode 3, the" modulatedLfradio frequency=fvoltageQ9 '-is L'converted intoaipositive'pulsatingdirect-voltage 31s, vas"-b`efore"ex a 'plaineduin the discussion'offthelroperation ofthe f system f 1 of Eig; V4. .'Thevoutput ciir'cuit- 2 '411 is lconnectedhthrough' 1;- capacitance-resistance zcouplingh to ar'pair lof l'balanced alternatingcurrent iamplier wacuumtubes- X41-:andi 43. Thefioutput flea'ds" 2; and ile-are "-'respectively -connected 'vlthrough condeu'sersr 33 'and 37 a'ndfresistors 35 V'and""`39 'Sto-'the' respective'finput.circuitslof 'tubes 43and 41. The "resistor`35 vis'.connected.betvveenlthe control-'grid 4electrode4 53 and the cathode -151 10ft lthe tubef43, and-therefsistor'39 isconnected betweenf the controlgridelectrode f 47=and the'cathodel'49 of' thetube- 41. l'Acommon biasing battery or other source B1 may be-usedto biastthe 1 control-grid' electrodesl 47 fand53 inegativelywith respect .--toithei1= associated eathodes 49 'and' 5l, :thusA to'rnaintain :'.the tubes 41 andl 431normallyv cut-oit. l To' 'attainx these .'lends, the positive terminal lof the .biasingfsource'iBi'i is n shownficonnectedto a' common-1junctioriJ ofthe cathodes "w49` andSLand the negative' terminalI isshown-connected 'to a junction of thelresistors 3Sfan T'39. `The-iplates 45 :aand '55 of the respective-tubes 41-f`andl43emeV connected :through corresponding platelloadsA 57fa'rid l`'59 to :the posi,- tive terminal' ofv af 'common plateesupply rbattery or other source B2; rthe' negativeA side 'of-Which is connected 'to the fzsaidfjunction of 'thecathodesl-49and` 51. For the case' 5of y the' electrode 9 located at theV centerfof tube I'Qthe'f'resulting' positive .impulsesy '31u/'ill produceacrossf'thereirent level as' a result o-passagei'throughfthe'coupling condenser I37, `periodically l@to drive-theigidf'of' the 'Y'.-tube l41' positive withrespect to1-the -cathode49,'fthe'r'eby t to -oyercornethebias ofthe'batteryBi. Sirnilar1y;'tl1e =''tube' 43' willbe'periodicallyy renderedconductive in antiphase. Across the plate loads'57 a'r1d"59l of'the tubes VAF41 land 431',` therefore,4 there will appear no. 'resultant 4'volt- -'1age. v'When," hoWever',-= the "ringy electrode 9j istmoved 'clos'er to 'one'fof' *the principal 'electrodesj than the" other, i fthe 'corresponding=anfiplier= ytubefi or 43"vvill' conduct -"'n1ore than the other amplifier-tube,x producing across'the :r'plate loads 57y andl 59, `between 'thefterminals :695 and '71, .1accordingly, amplifier direct-currentf impulse voltages ".'67 A'meter M connected between-the terminalsz'69 and 71'my ftherefore'findicate lnot only" the am'p'liiedmagnitude `oi 'the' 'resulting 'ouput Ivoltage `A67,' indicating the amount of displacement 'ofi the ring electrode? 9 from the center' 4of the tube 1, but also the polarity 'orldirect-current'level of the impulsesl 67,' which indicates toward'which principal electrode the electrode-9ihas'f'be'env displaced. `If,' '-on; the lother hand, the Iel'ectrode 9` is'-m`oved closer tothe -other'- principal electrode, the' ampliied'impuls'es in-the meter'M will beI of'polarity'oppositetothat'shownat '67.

It is -to bey understood-that'the-'meter-'IM maybbeireplaced by a conventional."cathoderayitubet indicator;

'thyratron control tubes, asiv later discussed in connection with the embodiment lof Fig-39, ornanyfother.desired control circuit, indicator or load. `Notwiithstandingffthe vlpresence of a superimposed' directcurrent voltageievel, -the amplied output infall:caseswilli-indieatefnotnonlyff the magnitude of displacement of'the ringrelectrodef 9, Abut also its direction of'displacement. r:"lihe'fcircuitf'of Fig. hasbeenl :operated i with a'fsmall'i neonftubeitrans- 'f ducer 1 Y'and vwithv standard'balancedfampl'iers 41and 45,V 1 producing extremely high' sensitivity.

f: AIt"haszprevimisly' ibeen'tnientio'ned A:that: athe: 1 principal ifielectrdesvmayxhaveany tdesiredicontiguration for shape. We have, for example, su'ccessfullyliemployedlatdisc felectrod'es: as'lillustrat'edl in.' fFig.f..1,'= wire electrodes. dis- 'f= osedpara'llel tothe'axi's oflthe tubeasillustratediinvEig. .'28,\.rod f electrode'sxand 'other ele'ctrodel structures. t? Varia- .:tion'sf in= theisensitiv'ity fof; the. tubeg'Hinfthef-rangeofmlinear fffoperaton of the tube'; inlthei'imaximum' output-"voltage Nimaia ofi the 'tube;fand1:ain` iotherl characteristics',- 'ofcourse cour with- 'difere'nt.'='electrode de'si'gnsandlspacings. CfUnder certain conditions; theisensitivityot 'the' :tube y'appears to V:decreaseasdthetspace 'between the electrodes is' fdecre'ased. 'l The:sensitivityl'ofthe;tube,rinlgeneral, appears-:tofi'ncrease '1' vvithzthe fincre'ased. lectrode'lfsurfa'ce area. lhef'refererice -V vi or initial :voltage Tinv :the .outpuv 'circuit-l andlftheffvaluef of Minimi-also vvary lwithelectrodelspacing.

1i Movable electrodes .lof-1- any,v desired 'shape'fmay alsoffbe .ff employed. JYarrow' circulari ringsl-such -as`f shown 'ati 9' in Fig. 1',-'wi'dercircular-hands; wire-meshieleotrocl'es, ring v-f;'fsegments;: .tlatmetal electrodesglf'pointed' electrodes and 125 f1 cipali electrodes spaced 'about 60 '-mm'naparteand operat- '405-'point" JB, this'I last-named characteristic'curveglin additionf-fthe' :magnitude iof l the v voltageV=decreased-fsharply with: movement? lof I Ithe' movable'- 'electrode as shown' in I'Fig..2. "'For': further electrodemovement, I"the'-'\/`o1tage .'ichangedmpola'rityand then" aisecond l`pointfof"voltage i Iinversion wasl lobtained. "The" pointed' "movable elec- -ff11trode, thereforefmightf be fused where it isdesired -to have several points of inversion, while theiconiplete'ring 'forfband electrodecould be used to'provi'deflong and-'sensitive? lineari .characte'ristics. l

'Depending'upon the needs ofthe'fapplicationtojvhich fr'the .'prese'ntlinvention lis i to' be put; furtherr'ntire;`r envelopes of :diierent fshape; length l and" 'cross-idirnensons' yand c'on- '.fztaining "different gases' or other ionzable 'medianiayfbe .iiused',1's' previously' discussed. At microwave" frequencies, ,--f as a further example;- the tube dimensions or'felectrode iispacin'gs mayl beconvenientlylmade resonantto the'tfre- 'quency 'ofithermicro-Wave field,

l Variations inp'otentialgradients-Withinthetube may #alsof 'be *produced* electrically; asf by `"connecting the: tube into'two' arms "ofa'fva-riableimpedance bridge ircuite'of f" the'type'fr describedfi ""thefy saidc'opending-l -application 'and "iil'lustratedlin"Fig.v` 7. :f-'Aitinyffipeatypewneon tube lifor example, having internal electrodesschematically shown '.'fat'3andl5,'hasf been found admirably sited" to the pur- 65'Jfposes ofLthe p'res'e'ntf"-inv'en'ti`on,' vvhenf'provided 'vi/ith* 'an external.' metal-band l electrode 9. 5 The alternating-'field e'generatori-17,flhaving ya voltagesuflicient to"A io'nizethe ;-tubef1,::m'ay "be 'l'conn'ecte'd by -conductor 7 3-` to" the exft'ernalel'e'ctr'o'de 9, and' 'by a conductor '75 tovl furtherfc'onput circuit of the bridge. Conductor 77f-isf preferably connectedl through: a 'condenser C2 tof the' ffprincipal electrode 5; 'and' conductof79- i'spreferably` connected through a; condenser. Cr tofther-principal' electrodev .3. :".Thed'irectcurrent: -output icircuit -2-'4 is? shownconncetcd y@across theeprincipalielectrodes 3&Ia'nd5.

f-Assume-frst, futhat'i thevbridge'iarms I :Containingfcon- :rdens'ers C1 `"and: `C2i have 'equal'A ca'pacityzfand th'ati'the ielectrode 9 is maintainedr xedliin a'f'position? preferably i301- 'syminetrical'tvs/ith?A respect to the' principali L electrodes 3 :fand 5. i The' :principal .telectrodesr 3l'fa'nd 5- Aare.; tlien at "lthe'asame 'falternating-iield streiigth'" with#respecty tothe electrode 9 because of theYphysicalrfandieleetrical' sym- '.-iin'et'ry Iof 4'sthe'rprincipalmelectrodes i vand lf-theie'leetrode 9.

electrodes 3 and 5 and there is then no output voltage V in the output circuit 2 4. Any desired initial resultant current and voltage nay, of course, be produced by appropriate initial physical or electrical asymmetry. If, now, the value of the capacitance C1 is changed, say an increase, the impedance between the principal electrode 3 and the electrode 9 decreases. The glow discharge between the electrode 3 and the electrode 9 becomes stronger than the discharge between the electrode and the electrode 9, since the potential gradients between electrode 9 and each of the principal electrodes are no longer of equal magnitude. A resultant current ow from the electrode 3 to the electrode 5 thus takes place and a positive direct-current voltage V appears across the output circuit 2 4, as indicated. This has been found to be substantially equivalent to displacing the movable electrode as described in connection with Figs. 1 to 6. The creation of more intense glow discharges between one of the principal electrodes and the electrode 9 may be observed in the tube as occurring in exactly the same manner as when the electrode 9 itself is physically moved.

Regions of substantially linear relationship between the change in capacitance C1 or C2' and the resulting change in direct-current output voltage V have been found, similar to a portion of the region A-B shown in Fig. 2. Since diiferent magnitudes of radio-frequency voltage from the source or generator 17 result at the electrodes 3 and 5 because of the diifering impedance elements C1 and C2, however, the actual voltage V appears to be a half-cycle voltage pulsating between zero volts and a maximum unipolar peak value dependent upon the amount of impedance diiferencey between the elements C1 and C2. If C1 is greater than C2, the pulsating voltage rises positively from zero volts, while if C2 is greater than C1, the pulsating voltage rises negatively from zero volts. The output voltage of the circuit of Fig. 7, therefore, may in same cases actually be amplified in alternating-current amplifiers without the need for modulating the generator 17 as discussed in connection with the electrode-moving systems of Figs. l, 4 and 5. The generator 17 in Fig. 7, however, may, if desired, be modulated to produce the above-described output voltage V following the modulation envelope. In the system of Fig. 5, for example, the condensers C1 and C2 may be varied, as shown in Fig. 7, instead of or in addition to moving the ring electrode 9.

In the graph of Fig. 8, the sensitivity of an experimental bridge circuit employing a tube similar to the tube shown in Fig. l in a circuit similar to that illustrated in Fig. 7 is plotted. A ZS-megacycle oscillator frequency was employed in this test and the variation of voltage V with various settings of the capacitance C1 was measured for different fixed values of C2. A sensitivity of about one volt direct-current voltage output per 10-12 farads capacitance change was obtained in this test. More sensitive results have, however, been obtained. The sensitivity, furthermore, was found to be substantially independent of the iixed position of the electrode 9, within certain limits. With an amplifier having a noise level of about 10-5 volts connected across the output circuit 2-4, changes in capacity of the order of 10-17 farads may be detected.

lf, therefore, the variable condenser plates C1 are moved, oscillated, or rotated to produce more or less capacitance, as hereinafter discussed in connection with the systems of Figs. 32 and 40, as illustrations, the same effect takes place in the tube 1 and in the output circuit 2-4 as is produced by the movement of the electrode 9 in Figs. 1 to 6. The circuit of Fig. 7, therefore, may be employed in the same manner as those discussed in connection with the embodiments of Figs. 1 to 6. It is to be understood that whatever the motion of the electrodes will do in the embodiments of Figs. 1 to 6, the variation in impedance, shown as capacitance, of the circuit of Fig. 7 will also do. The use of capacitance variations, moreover, permits the universal use of the circuit with discharge media of any desired dimensions and shape and provides, also, the advantages of easier7 more convenient and more accurately controllable opation. Though various devices employing these circuits have been and are hereinafter illustrated in the present application as applied to one only of these embodiments, this is only in order to simplify the disclosure,

for these devices may similarly be embodied in the circuits of the other embodiments.

It is not necessary, however, that the circult of Flg. 7 be limited to capacitances alone. Any impedance means may be employed, such as, for example, reslstors or 1nductors, not shown. Non-linear impedance elements such as photoelectric cells or mosaics may also be employed, since sensitivity calibration curves may be used to interpret the output voltage V.

An unknown capacity C2' may be readlly measured 1n the simple bridge circuit of Fig. 7 by Varying the capacitance C1, as previously described, to produce a deslred reference voltage. It is sometimes preferable, however, to employ a known iixed capacitance C2 and to insert the unknown capacitance in place of C1. The value of V obtained would then yield the value of the unknown capacitance from a calibration curve similar to those 1llustrated in Fig. 8. This method of measurement is particularly valuable in determining the value of very small capacitances or in measuring condensers to a high degree of accuracy.

If the elements C1 and C2 are both variable condensers whose movable plates are 180 degrees out of phase and mounted on the same shaft, as later described in connection with Fig. 40, or if they cooperate with a common movable condenser plate, as later described in connection with Fig. 27, so that an increase in C1 is accompanied by a corresponding decrease in C2, providing differential capacitance operation, double the sensitivity may be obtained. As the impedance between one principal electrode and the electrode 9 decreases, and the potential gradients therebetween are correspondingly increased, the impedance between the other principal electrode and the electrode 9 increases instead of remaining at the same value, with a corresponding decrease in potential gradients. A greater sensitivity still may be obtained by mechanically ganging or otherwise moving condenser plates in synchronism with the movable electrode 9, as explained in the said copending application, to provide a four-way control over the sensitivity of the tube. The invention is not, of course, limited to the sensitivity provided by a four-way control, for there may be additional variable impedance elements, as discussed in connection with the systems of Figs. 13 to 16, as wcll as additional movable electrodes, as beforementione With the external variable impedance or other means for varying the potential gradients within the tube, such as disclosed in the bridge circuit of Fig. 7, the electrode 9 may be disposed within the envelope 1 and the envelope 1 may be constituted of conducting material to shield the tube from stray fields and even to constitute a cavity resonator.

One of the important features of the present invention, before mentioned briefly, is that over relatively wide limits of position of the electrode 9 or variation of the capacitance C1 or C2, the operation of the various embodiments of the invention may be substantially independent of voltage or frequency variations of the oscillator or generator 17. The direct-current output voltage V has been found to remain substantially constant over a broad band of operating frequencies or wavelengths of the oscillator 17, for a given position of the electrode 9 of Fig. 1 within the limits A-B, Fig. 2, or for an adjustment of the capacitance C1 or C2 in Fig. 7. A constant response, for example, from about 28 meters to about 82 meters wavelength was found in one test with an 80-volt alternating lield and a helium gas-filled tube under 1.98 millimeters pressure. While the length of the linear portion A-B of the characteristic curve, however, rnay sometimes vary with frequency, so that Vmax may be different for different frequencies, frequency bands have been found over which a substantially constant Vmax may be obtained. In a further test with the above-mentioned tube, for example, a constant Value of Vmax was obtained from about 15 megacycles to about 45 megacycles with a slightly lower alternating eld of 75 volts R. M. S.

Variations in R. M. S. voltage of the oscillator 17 within certain limits similarly will not aiect the voltage V. With the location of the electrode 9 of the tube discussed in connection with Fig. l at the 21.8 mm. point, Fig. 2, for example, the R. M. S. value of the 26.5 megacycle oscillator voltage may be varied from 150 volts down to volts with no substantial change in the value of- :the' outputvoltagey V. Over substantially thesame: range, the sensitivity of the tube .remainssubstantially f constant, also. Withl-vtheelectrode 9 close yto oneof the principal. electrodes, however, variations of the .'voltage.

V with-,voltage of the oscillator have been detected;

Operation'within the frequency bands andthe voltage..A

bands overwhich the. .system is substantially'independent of Yfrequency andvoltage,.is extremely valuablein the bridge circuit embodiments of'the presentyinverition;

Noneof the usual compensating circuits` orwreiinedl control circuits are neededto prevent vfrequency Vdrift/or i variationsl in voltageof the alternating current. generator that -upset the calibration of conventional bridge .cir-:-

cuits.

If, on the other hand, it is desired purposely to increase.:v

or decrease `the sensitivity of the tube by varying .the-frequency, .frequency bands have beenzfound over which anincreasein frequency, as an illustration, willproducel an increase-in the slope of the v.characteristic curve A-B tween voltagelimits within whichy the' value. of Vmax Viri-` creases `with increasing R. voltage-.of the oscillator 17.- We have found, as an illustration, a substantially linear variation-of Vinex-with an applied alternating-cur-v rent field of 26.5 rnegacycles frequency ina tube of helium under. 1.60 mm; pressure.: This variationy was from- Vmax=l2.5 volts at V108 volts R.- M. S.,to Vmax=40 volts at 146 volts RAM. S.

By adjusting the-frequency or they applied voltage,-

therefore, operating regions having alniost'anyy desired characteristic, including substantially constant,-linear,` square, cubic or exponential characteristics, as illustra-V tionspmay beproduced. The selection of the gas, the' gas pressure, the electrode structures, the' positioning; of

the electrodes,` the tube dimensions, etc.,l afford .further I meansfOr producingthe desired sensitivity and response,

as previously discussedindetail."- The presentl invention thus -provides vfor 'extremely eXible systems.

If the electrode 9 be omitted, and the tube 1 with-its|` principall electrodes and S be properlyoriented in an alternating electricfield suflicient tofstrike :a glow-inf the tube, as discussed in the vsaid copendingapplication, such as, for example, in-,tlieV iield between the fixed externa-l :plate :auxiliary electrodes 81 'and 83 .of Fig. 9

or -in a radio-frequency radiation field, lthe *direct-cur rent voltage V will be produced in the output circuit- 2-4 Whenever one principal electrode is subjected to a higher electriceld strengt-hlthain the.- other lprincipal electrode.y Theenvelope 1, as an illustration, `maybe oriented with its long axis substantially parallel to the lines of electric force produced kbetweenvthe two 4preferably xed condenser `plates 81 and 83,shown vertical forV purposes-of illustration. When the'uenvelope 1 is they two principal electrodes 3 and15 will be at the same fieldstrength, and potential gradients of equal symmetrically located between the plates 81 `and "33', 60A

magnitude will.v be developed between the electrode' 3 and the center yof the .envelope 1 vand between the elec- A uniformy trode 5 and the center of the Venvelope 1.' ionization glowV will-be struck through the envelope and noresultant direct-current voltagefVwillbe produced inthe output` circuit` 2-4. envelope, 1 is moved downward, for example, the electrode 3 will be subjected to a higher field strength than the yelectrode 5, and the potential gradients between each electrode and thecenter ofthe tube ywill no longer be the same. The glow discharge in the lower portion of the envelope 1 will be brighter than' `the glow dischargek in the-upper portion of the tube'. A resultant current iiow will thus take place in the tube 1 from the electrode 3 to the electrode 5, producing a positive voltage V vin the output circuit 2 4. Similarly, if the-tube -1 be moved upwardwithin the alternating field, a negative voltage V will be produced. The characteristic performance of such a system will correspond to that -shown in FigstZ and S as Vthe tube is moved up and down in the alternating field. This is-fully equivalentttofvaryingthe condensers Ci and-.C2 in Fig. 7

As, however, the

since;.capacitance-.exists between ythe electrode-.g5 :and-.ii the -lelectrodeySl andV between Ithe electrode and the if electrode 83, corresponding, respectively, totthe icon-g.. densersCi and C2. It shouldtbe-understood,fof.courseya` that. it is `tlie'relative movement lof. the-tube 1 anduthe-yelectrodes 81 fand 83 that isimportant, sogthattthev electrodes 81 and 83 mayLequally-well bemovedg-rela-f.. tive-toa fixed tube 1.

With,= for example, Va ten ymillimeter -tube,;1,.:havingf;. wirey electrodes 3 and. 5 spaced yabout 30:millimeters-f; apart and iillednwith Iargon .gas.,at.;,a pressure, of iabouti 0.8 millimeter, l and l .withI an SOOfkilocycle-f generatorf17w of. about 5.5 watts :output,vdirectcurrent1outputfvoltagefg; sensitivities vhave, been'obtained .in excess-of 500.volts; per millimeter -relative movement=ofthe-.auxiliary elecfttrode platesf81,` 83..and the= tube-1.

A convenient radiationeld-strength indicator is :thusitg also provided; which produces a direct-currenttindicating voltagel in response.tovariationsfin field strengtln- Over a predeterminedrange, furthermore,- a linearrelationewship lbetween :field strength and the .direct-.current-in-n. dicating voltage may be obtained...` By-operatingtthe, tube 1 on a portion of.itscharacteristic-curveaovervwhich an approximate `square-.lawfvariation..occurs,sucli` as-t;l in the. region of thebends. inthe farleft-hand or right-` liand portions of the curve shownin.Fig. 2, a voltage-fproportional, to. the. energy or poweimofgthe .field lmayer; be produced..` The direct-.current level upon which-the-V output voltage Vis superposed, .further-more, may,.be.- adjusted to.anyA desiredvalue as, for example, .with.the., aid of biasingelements 85 yand 87,. -as may. the level... of the output voltage` of all of ,the.other. embodiments of .the present invention. Bye this. expedient; further more, a unidirectionaloutput. may .be obtainedregard-f. less of whetherthe tube 1 movesV in one..,direction ,or-the... other. If the generator 17 is of themodulated-type,..- as discussed-.in connection with, theusystemsvofFigs,... 4 and 5, the Ioutputvoltagewill.comprisea superposif. tionof the voltage of thebiasing elements85for.87 and the pulsating .voltage 31.

If the tube 1 is .oscillated .between iixedelectrodes 81,.. and 83, as .by connectingit to Aany desired vibrating', means such as, for, exainple.k to vibrators fofgthe type. hereinafter described in connection with. the; embodV-f.. ments of Figs., A32er 47,` an oscillatingvoltage .willfrresult inthe output circuit 2-4.of frequency dependent.. upon the frequency of the movement of the;.tub,ey 1, and... of peak magnitude determined by the-,furthest .displacement of the tube 1 lfrom symmetry inthe eld prof... duced between the electrodes 81 and 83., If,;further.. more, the generator 17 is modulate.d,l.as.discussed.in.. connection with Figs. 4 and 5, then a beat frequency... resulting from the mixing of the pulsating,modulation.... direct-current voltage 31 and the mechanical .oscillation-, frequencyof the tube 1 will result' in the output circuit... This mode of operationhas particular advantagefwhere i variable modulation of the oscillator 17may1beemployed4 and where. it is desired to obtain the .frequency of. mechanical oscillation of the tube 1 by the beat frequency` before mentioned, The beat frequency is ari,indication.:; proportional to the difference of the .mechanicaloscillatf Y ing frequency ofthe tube and the modulation frequencyv of the radio-frequency source 17.

In Fig. 17, `external wire or: rodauxiliary eldelectrodes V,81 and 83, areemployed -insteadof plate elec. vtrodes, to provide ,a `'symmetrical' eldwith respect to'.

a horizontal line, shown .dotted,..connectiiig the centersf: of the external electrodes 81 and 83.- With wire-princi. pal electrodes 3 and 5 of .the tubeml `disposed sym-vr .,metrically with respect to the dotted horizontal lirie,-y

hand, will cause different iield strengths to be set up- :the external electrodes S1 and 83, above and below the said horizontal line, is not linear, but, rather, varies in accordance with a function determined by the geometry of the system, (in this case, producing kthe wellknoWn'electric-intensity pattern occurring between paral- `85flelwire^ transmission. lines,4 as discussed, for example,

on pages 47 to 57 of Electric Circuits, M. I. T. Staff, John Wiley & Sons, 1940), the magnitude of the output voltage produced upon vertical displacement of the tube 1 is also dependent upon the horizontal position of the tube in the direction of the arrows 113 from the center of the said horizontal line. The polarity of the output voltage is dependent on the direction of vertical displacement with respect to the dotted horizontal line. This system, therefore, provides for producing voltages representative of displacements of the tube 1 and varying in accordance with a function of two directions of motion or displacement, such as, for example, in accordance with the product of the motions in both directions.

By properly shaping the auxiliary electrodes 81 and 83, moreover, or otherwise modifying the field between them, the output voltage may be thus related by any desired predetermined function to the displacement, position or motion of the tube 1. lf, for example, the electrodes 81 or 83 or both are shaped to produce an electric field representative of a predetermined function, movement of the tube 1 in the field in one direction will produce direct-current voltages varying in accordance with the said function. In the system of Fig. 18, as an illustration, the auxiliary electrode 81 is curved upward in accordance with a predetermined function, such as a square law. The principal electrodes 3 and 5 of the tube 1 are shown end on as wire or rod electrodes, the longitudinal axes of which are oriented substantially parallel to the plane of the bottom external eld electrode 83. Horizontal and vertical movement of the tube 1 in the special function field distribution between the electrodes 81 and 83 will produce a directcurrent output voltage in the output circuit 2 4 Varying in accordance with the function. Linear horizontal movement, for example, may produce a voltage related to the square of the movement in the illustration, above. This may be considered an electrical analogue of the mechanical cam system of Fig. 6, before discussed.

In all of the transducers previously discussed, only two principal electrodes are employed. As discussed in the said copending application, however, more than two electrodes may be employed. If, for example, more than two principal electrodes are employed, two or more direct-current voltage outputs may be obtained indicating, for example, displacements or motions in two or more directions. In the system of Fig. 19, as an example, a pair of vertically disposed electrodes 3 and 5 will produce in the output circuit 2-4, direct-current voltages measuring the direction and magnitude of the vertical displacement 115 of the normally vertically centered tube 1 between the plane horizontally disposed external vertical-field-producing auxiliary electrodes 81 and 83 energized from a generator 17. Similarly, a pair of horizontal electrodes 3 and 5' in the same transducer tube 1 will produce in the output circuit 2 4 direct-current voltages measuring the direction and magnitude of horizontal displacement 113 of the normally horizontally centered tube 1 between the plane vertically disposed external horizontal-field-producing auxiliary electrodes 81 and 83', also energized from the generator 17, or if desired, from a separate generator. Displacements or motions of the tube 1 in two dimensions are thus selectively indicated. It is to be understood, of course, that, if desired, one of the electrodes may serve as both a horizontal and a vertical electrode, in which case only three electrodes would be necessary instead of two pairs of electrodes. In the same manner, a third pair of electrodes, not shown for purposes of simplicity, extending in a direction parallel to the plane of the drawings may be used to indicate displacements in the third dimension out of the plane of the drawings between a similar pair of plane external auxiliary electrodes, also not shown in order not to complicate the drawings, disposed in planes parallel to the plane of the drawings. Displacements or motions in any direction or coordinate may thus be independently indicated. The fields between the external auxiliary electrodes 81, 83, 81, 83', etc., may, furthermore, be modified in accordance with any desired law as before explained in connection with the systems of Figs. 17 and 18, and they may be of any desired configuration. If, as a further illustration, the generator 17 feeds radiofrequency energy to the electrodes 81 and 83 in ninety degree phase relationship with the energy fed the electrodes 81 and 83', a circular field pattern may be established in which the tube 1 may be moved or displaced. Other phase, amplitude and frequency relationships between the fields set up between the various pairs of external electrodes may, of course, also be employed as is well-known in the art. In the systems of Figs. 9, 17, 18 and 19 above discussed, and also in the system of Fig. 11 hereinafter described, furthermore, it is to be understood that instead of moving the transducer tube between the fixed external field-producing electrodes, the transducer may be fixed and one or more of the external electrodes of each pair of fieldproducing electrodes may be moved relative to the transducer, thereby to produce the same results.

A system fully equivalent to that of Fig. 9 in which the tube 1 may also remain stationary is illustrated in Fig. l0. Condensers Ci and Cz are shown respectively replacing the capacitance between the principal electrode 3 and the auxiliary electrode 83 and between the principal electrode 5 and the auxiliary electrode 81, the condensers C1 and C2 serving, also, as the auxiliary electrode means. By varying or vibrating the Condensers C1 and C2, the same effects above-described in connection with movement of the tube 1 may be produced. The Condensers C1 and C2 may also be replaced, of course, by any other impedance elements.

Enough has already been shown of the many similar and equivalent arrangements that the transducers of the present invention may take to establish that whatever movement of the tube or of the tube electrodes will do in particular forms of the invention, movement of a capacitor or other impedance element or of field-producing-elements will do in other forms. All of the forms of the invention are interchangeable and a showing of one form operating in a particular manner or with a particular device is to be understood as only for purposes of illustration, since every other form of the invention may be similarly operated in the same manner or with the same device.

If a circuit resonant to the frequency of the oscillator or generator 17 is connected in the output circuit 2 4, very desirable results are obtainable. The resonant circuit, it is to be understood, may be employed in the output circuit of any of the embodiments of the invention, but for convenience it is illustrated in Fig. 11 as applied in the output circuit 2 4 of the system of Fig. 9. The resonant circuit is shown comprising a parallelconnected condenser C and inductance L shunted across the output terminals 2 4. A condenser 89 is placed in series with the inductance L to prevent a short circuit of the direct-current output voltage resulting, in accordance with the present invention, between the electrodes 3 and 5 in the output circuit 2 4. Either the condenser C or the inductance L, or both, may be tunable, though, for illustrative purposes, only the condenser C is shown variable. If the resonant L C circuit of any desired form, such as lumped circuit elements, a piezoelectric crystal circuit or a cavity resonator, is tuned to the frequency of the generator 1", a radio-frequency voltage, for example, will arise between the principal electrodes 3 and 5 that is dependent not only upon the capacitance between the principal electrode 3 and the auxiliary electrode S3 and between the principal electrode 5 and the auxiliary electrode 81, but also upon the electrical. characteristics of the L C tuned circuit. Varying the tuning of the L C circuit above and below resonance to the frequency of the generator 17 changes not only the magnitude of voltage between the principal electrodes 3 and 5 but also the phase of the voltage with respect to the voltage between the external electrodes 81 and 83. This variation of phase, furthermore, further varies the field strength in the vicinity of the principal electrodes 3 and 5, thereby influencing the magnitude and polarity of the direct-current voltage arising in the output circuit 2 4.

The graph of Fig. 12 illustrates an experimentally obtained curve relating the direct-current output voltage V as a function of the tuning of the condenser C in the L C circuit. As C is tuned to cause the L C circuit to approach resonance with the frequency of the generator 17, the voltage V rises as shown at 91. Closer to resonance, the output voltage falls sharply, as at 93, passing through zero at the resonant point 95, and reversing polarity to increase sharply negative, as at 97, below resonance. Further variation of C' to tune the anamnesi LCi-.circuitfurther below .resonance'results inla more gradualzdecrease 99 in negative outputvoltage.:

anygfof.-theembodiments ofthe present invention, therefore, provides-.for the developing of a direct-current output;;.voltage:.that depends both upon-,the adjustment-.of

the I.transduccrcircuiti itself, such vas the displacement of thegelectrode19 in Fig. Al, or, the lvariation of the capacitor Cr.of1-Fi'g..7, or thetrelative positioningof the tube and` the; external .held-producing .auxiliary electrodes ofl Fig.

9,'-. and.v the-tuning of the output resonance 1 circuit.` Eitherthe ,adjustment of the transducer circuit or the tuning .of the outputv resonance circuit, or both, may be used for position-indicationmeasuremena control. purposes,-or'for. anyof thevarious applications of the presentginvention.;A Of lparticular interest, for. example,'-is the useasofosuch system for resonance indication. Presentdaywvoltageaor.current resonance indicators respond to thenrelatively atz resonance response of tuned circuits. The-.presentinventiomon the other hand, at resonance, passes sharply through zero output voltage V, as shown at- 95gzpermitting .very accurate resonance measurements.

Thegfact,'moreover,;that theresponse shown in Fig. 12

in the output ornto'.V a conventional reactance tube, in the manner illustrated-ain Fig. 24, for example, to keep the center. frequency. of frequency-modulated transmissions constant, as is Well known in the art. The use of this circuit provides, as .still another illustration, a direct measurement of phase angle because ofthe characteristic of Fig. 12.

The output-circuit tuned circuit L-C may also be tuned-.to the frequency of any modulation envelopevof the"radiofrequency or vother carrier energy of the generator .17, as previously discussed in connection with the systems of Figs. 4 and 5, or it may be tuned to the relative vibrational or oscillatory frequency of the tube 1 and external field auxiliary electrodes as discussed in connection with the embodiment of Fig. 9, or to the.

relative: vibrational .or :oscillating frequency of the ring auxiliary electrode 9 and the principal tube electrodes of.;Fig.'. 1, orv the frequency of movement of the condenser C1 or C2 of Fig. 7, and so on.

Before commencing detailed treatment of specic applications of the transducer circuits of thepresent inventionyit is desirable to mention several other illustrative1 forms that. the invention may take. ln Fig. 13,

for'exarnple, a tube 1 having principal electrodes 3 and 5 is operated in a manner similar to that discussed in connectionwwith Lthe embodiments of Fig. 10 with the aid of a plurality of impedance elements arranged in the formof a bridge. This circuit is of the ungrounded type.`v .Impedance elements 101 and 103 are shown connected .in series with the generator 17. Two further series-connected impedance elements 105 and 107 are connected in parallel with the elements 101 and 103. These impedance elements, like the condensers Cr and C2 of FigplO, also serve the function of auxiliary electrode means. The principal electrode 3 of the tube 1 is connected to the junction between the series-connected elements 101'and 103, and the principal electrode 5 is connected to the junction of the impedance elements 105 and. 107. The potential or eld strength of the electrode 3, with respect to some reference, perhaps ground, is determinedby the ratio of the impedances of the impedance elements 101 and 103,while the potential of the electrode 5 is determined by the ratio of the impedances ofthe impedance elements 105 and 107. Differential potential gradients may thus be set up by adjustinggthe respective ratios or" the impedances, producing etectsin the output circuit 2 4 of the same character asthose obtained when the tube 1 of Fig. 9 is moved between the auxiliary electrodes S1 and 83, or when the condensers Ci' or C2 of the tube 1 of Fig. 10 are varied,

As a specific-illustration,a double capacitoris -shownf is the impedance elementt101gswhile the capacitance'between theacenter condenser plate .102 .and the fbottom'f condenserplateis1thelimpedance. element-':103; Wit-fri` ther center-plate 102 A.half-.way between fthe Aupper-rand lower condenser. plates, the impedancessltiland 103 are equal. Movement of the center .plate-.102 'toward, ';'fo'r== example, the l.upper condenser plate, increases lthe-ca.-L pacitance ofv impedance elementrr101; correspondinglyI I decreasing thecapacitance of .impedance.element103;PIK Impedance elements 105 and 107 may, as an-illustra'- tionfbe capacitances'each 'of value .equal lto'.-theboriginal values of impedance elements 1011and :103;"so--that-1the1' unbalanceof the elements101'andfl03produces'a fieldstrengthfdiiferential between'the principal-@electrodes f3 and 5 resulting in a direct-current output Vvoltageg Vlinw; the output circuit 2.4, ofv thel character previously deli scribed.

The modification of: Fig. 14 differs from the'circuitsw of Figs. 13 and` 16 onlyinthe .particular that 'anexternal ring -electrode-9 `is `alsoremployed connected Ito't-the junction ybetween impedance elements -103`and y10T-Yat a point of diierent potential than `the principal-'elec-y` trodes 3 and 5. Thissystem: may-therefore bysym=vmetrically or unsymmetrically grounded, or not grounded at all. Variations of vthe impedance elements 101,403?? and 105,107, serving the function Iof anauxilia1"yfele'c-- trode means, as before stated, and/or movement-fof the further auxiliary electrode 9 will produceoutput voltagesI as before-described. Instead of connecting thefexternal electrode-9 to the junction between the impedance ele-"iments 103 vand .107 as inv the system `ofFig.n 14;'more-rA over, the electrodeu9 may be connectedv to'ianyotherf point such as the junction between series-connected volt-t age-dividingV impedance elements. 109:*and 111,.; shown connected in shunt with the elements 101,' 103 -in'Fig-15f* The bridge circuits of Figs. 13 to-16', in the same manner as discussed before in connection Iwith the-equival lent basic bridge circuit of Fig. 7, may alsov beffused; among other purposes, for measurement of the value of* any of theimpedance elements themselves or of changesi .in the' values thereof. In the circuit of Fig.4 13, form' example, the value of an unknown impedance element"i 101 may `quickly' be determinedv by employing equal-"- impedance elements 103,105 and 107 'Sand merelytmeas-l uring` the value of the properlycalibrated direct-current voltage V in the output circuit 2-44.

Thetransducers of the present invention lend them-t selves also to circuits for measuring differential 'effects-f such as, for example, the difference betweentwo move-tv ments. More generally, the present linvention provides-1v a novel system for algebraic addition.y Algebraicraddiiigvf embraces the addition of positive quantities, the'-addi"' tion of negative quantities and the addition of fpositivef' and negative quantities, often called subtractionnA Init'- the embodiment of Fig. 20, as an illustration,*identical* gas-discharge tubes 1 and 121 are shown each providedwith respective principal electrodes 3, 5 Aand "123',"125"' and each provided with an external ring electrodet 9`ff and 129. A common alternating-current*source orfgen-- erator 17 is shown providing'energy to the-two tubes-1f and 121 by means of the same type of circuits previously described in connection with the embodiment of Fig. The principal electrodes 5 and 125 of the respectivetubesfV 1 and 121 are connected together toy one'terminal of@ the generator 17'. The other terminal of lthe'generatorVA` 17 is connected to the movable electrodes 9 and 129.?y The electrodes 3 and 5 are coupled by a condenser 117'" and the electrodes 125 and 123 Vare coupled'by a con-x denser 119. Between the principal electrode-3 ofthe; tube 1 and the principal electrode 123 of they tube 121,'. is connected an output circuit 2 4 -embodyingasfan f: illustration, the meter M. A direct-current potentiall may arise, as before explained, .betweenthe principahf electrodes 3 and 5, the magnitude and polarityof which depend upon the direction and amount of displacement of the ring electrode9 fromfthe centerof the tube 1.' Similarly, a direct-current voltagemay be produced .between the principal electrodes 123 and 125 of polarity.;v and magnitude dependentupon .the directionrandamountr.: of movement of the ring electrode-1295 fromrthe center t' "of'the tube -121'. If 'the-ring eltelctrode);for-example# is moved in the direction of the arrow placed adjacent thereto, the electrode will become negative with respect to the electrode 3. Similarly, if the ring electrode 129 is moved in the same direction toward the electrode 123, as indicated by the arrow adjacent thereto, the electrode 125 will become negative with respect to the electrode 123. Since the electrodes 5 and 125 are at a common potential, being connected together as before described, a voltage arises between the principal electrodes 3 and 123 that is dependent upon the difference of position of the ring electrodes 9 and 129 from the respective centers of their respective tubes 1 and 121. The circuit of Fig. 20, furthermore, is remarkably free of interacting influences between the tubes 1 and 121.

If, for example, both ring electrodes 9 and 129 are moved in the same direction the same amount toward the respective principal electrodes 3 and 123, the voltage appearing across the meter M, which, as before described, is connected between the electrodes 3 and 123 in the output circuit 2 4, will be zero. If, on the other hand, the auxiliary ring electrodes 9 and 129 are not equally displaced from their respective tube centers, and if the tubes 1 and 121 are operated over their substantially linear characteristics, the output voltage across the meter M will be proportional to the difference in the displacements of the electrodes 9 and 129. It is to be understood, of course, that the circuit of Fig. 20 is equally adaptable to measure angular as well as linear position differences, as when, for example, the ring electrodes 9 and 129 are moved in response to angular displacements, such as those discussed in connection with the embodiment of Fig. 3.

While the tubes 1 and 121 have been shown connected to the same source 17, it is also to be understood that the tubes may equally well be energized by separate generators, as when they must be operated at remote points. An application of such a circuit arises, for example, in remote-control operations where it is desired to have two movements or displacements maintained in synchronism. By the expedient of the circuit of Fig. 20, displacements at one ring electrode will produce in the indicator M, a voltage indicating the difference between the position of the displaced ring electrode and the position of the other ring electrode. Upon movement of the other electrode to the point where the meter M or other device registers a null, the two ring electrodes 9 and 129 will then be in corresponding positions on their respective tubes 1 and 121.

lf the electrodes 9 and 129 are not moved in the same direction relative to the centers of their respective tubes, but, on the contrary, are moved in opposite directions, a voltage will be produced in the meter M proportional to, or otherwise representative of, the sum of the displacements of electrodes 9 and 129 from the centers of their respective tubes 1 and 121. It is to be understood, moreover, that the preferably high impedance meter M may, of course, be replaced by any well-known follow-up circuit, as later described in connection with the embodiments of Figs. 34 to 36 to produce voltages that may be used mechanically to move the ring electrodes into corresponding positions on their respective tubes.

It will be observed that the circuit of Fig. 20 may be considered as a series circuit, in which the tubes 1 and 121 aid or buck each other in series with the meter or other indicator M. The present invention is not by any means, however, limited to series-connected transducer circuits. In the embodiment of Fig. 2l, as an illustration, two tubes 1 and 121 are shown connected in parallel. These tubes are operated as transducers in accordance with the principles previously discussed in connection with the embodiment of Fig. l0, in accordance with which a center auxiliary ring electrode need not be employed, but differences in potential gradients between the respective principal electrodes 3, 5 and 123, 125 may be produced by variable impedance elements, such as the variable capacitors 131 and 33, shown respectively connecting the principal electrodes S and 125 to one terminal of the generator 17 and acting, also, as auxiliary electrode means. The other terminal of the source 17 is connected to both the principal electrodes 3 and 123 of the respective tubes 1 and 121. rl`he respective principal electrodes 5 and 125, moreover, are shown each connected through respective similar isolating resistors 135 and 137 to one side of a meter or other indicator M, and the principal electrodes 3 and 123 are shown connected to the other terminal of the meter or the other indicating circuit M. It may be shown that, where two voltage sources, such as the tubes l and 121, are connected in parallel through identical isolating impedances, such as the resistors and 137, the voltage resulting in an output circuit shunting the sources of voltage, such as the circuit 2-4, is proportional to the sum of the voltages of the two voltage sources. The isolating resistances 135 and 137 are preferably of high value but the meter M may have any desired impedance. As the condensers 131 and 133 are varied in different amounts in response, for example, to movements that operate upon their condenser plates, as hereinafter discussed, the direct-current voltages produced in accordance with the phenomenon of the present invention across the principal electrodes of the respective tubes 1 and 121 will correspondingly vary, producing in the meter M a voltage which is proportional to bthe sum of the voltages produced by the two transducer tu es.

The present invention is not limited, furthermore, merely to obtaining the sum or the difference of two quantities such as two mechanical displacements or movements. It may equally well be applied to obtaining the composite sum or difference of any number of different quantities. In the embodiment of Fig. 22, as an illustration, three transducers, 1, 121 and 141, are illustrated, each supplied with respective principal electrodes 3 and 5, 123 and 125, 143 and 145. The tubes 1, 121 and 141 are shown provided with respective movable ring electrodes 9, 129 and 139. All of the ring electrodes are connected in parallel to the lower terminal of the source or generator of radio-frequency or other alterhating-current energy 17. The principal electrode 3 of the tube 1 is shown connected through a coupling condenser 147 to the upper terminal of the source 17, and also, through output-circuit conductor 2, to one terminal of an output meter or other indicator or voltage-responsive circuit M. The principal electrodes 5 and 123 of the respective tubes 1 and 121 are shown connected through a common coupling condenser 151 to the upper terminal of the source 17. The principal electrodes 125 and 143 of the respective tubes 121 and 141 are similarly connected through a common coupling condenser 153 to the upper terminal of the generator 17. The principal electrode of the tube 141 is also coupled by a coupling condenser 15S to the same upper terminal and is also connected through output-circuit conductor 4 to the opposite terminal of the meter M from that to which the principal electrode 3 is connected by the conductor 2. In effect, therefore, the three transducers 1, 121 and 141 are connected in series so that the meter or other voltage-responsive circuit M in the output circuit 2 4 will read various combinations of the sum or difference of the displacements of the ring electrodes 9, 129 and 139 from the respective centers of their respective tubes, 1, 121 and 141, depending upon the directions of displacement of the ring electrodes from the respective centers of their respective tubes.

In all of the differential or summation systems above described, it is possible to place the meter or other voltage-responsive circuit M at a point distant from the transducers. The output conductors 2-4 leading to the meter or other voltage-responsive circuit M carry directcurrent only, and may, if desired, be by-passed with capacitors, as is well known in the art, so that no pick-up or induction will result along the output leads. The embodiments of Figs. 20 to 22 may thus nd convenient application in the remote measurement of Various sums or differences of movement or displacement of different loads located at different points of a system. These circuits are useful also as adding or subtracting machines or counters.

As before mentioned, furthermore, the output circuit 2-4 of all the embodiments of the invention may be connected to any type of voltage-responsive circuit and not merely to a meter or indicator. In the system of Fig. 23, as an example, a single transducer 1 is shown, for purposes of illustration, connected with its output terminals 2-4 feeding the electrodes of a radio-frequency transmitter tube 157. The displacement of the ring electrode 9 produces voltages that result in varying the bias on the transmitter electrodes, thereby to amplitude-modulate the transmitter. If the transmitter 157 comprises a reactance tube, the voltage from the transducer may be fed thereto to vary the frequency or phase of the transmitter 157, as later discussed in connection with Fig. 24, so that there will be transmitted from the antenna 159, radio-frequency transmissions modulated by the voltages produced by the transducer of the present invention. These signals may be picked up in a receiving antenna 161, and demodulated in a receiver 163 for presentation in, for example, a meter or other indicator M.

While a separate generator 17 is shown provided for energizing the transducer 1, the radio-frequency transmitter 157 may be used to excite the transducer as well as to provide radio-frequency energy for transmission into space. As illustrated in the embodiment of Fig. 24, a common radio-frequency generator or source 17, accordingly, is shown feeding radio-frequency energy to excite the transducer 1 and to energize a resonant or tank circuit consisting of, for example, a parallel-connected condenser 165 and inductance 167. The resonant circuit 165-167 may, of course, comprise any radiofrequency tuned circuit such as, for example, a resonant transmission line, or a cavity resonator. The energy in the tuned circuit 165-167 may be modulated, as previously described in connection with Fig. 23, in response to the direct-current output voltage of the transducer 1. The tuned circuit 165-167 is shown coupled to the antenna 159 through an energizing coil 169. The ring electrode 9 may be positioned in approximately the center of the tube 1 and connected to some point in the output energizing coil 169. The principal electrode is shown connected to the grounded terminal of the source of radio-frequency energy 17, and the other principal electrode 3 is illustrated connected through a variable condenser C to a modulating device such as, for example, a reactance tube 171. The reactance tube may be connected to the tuned circuit 165-167 in conventional manner to vary the frequency of the radio waves coupled into the antenna 159. As the condenser C is varied in response to any desired force to produce an output voltage between the principal electrodes 3 and 5 in the output circuit 2-4, thereby to vary the impedance of the reactance tube 171 and correspondingly to eect the tuning of the circuit 165-167, radio waves are transmitted that are frequency-modulated in accordance with the amount of variation of the condenser C. As before mentioned in connection with the embodiment of Fig. 23, the output voltage from the transducer 1 may equally well phaseor amplitude-modulate the transmitter. By operating these systems over particular ranges previously discussed in detail, where the operation of the tube 1 is independent of variations in frequency or amplitude of the generator 17, though the frequency or amplitude of the radio waves varies in response to the modulating voltages produced by the transducer 1, as illustrated in Figs. 23 and 24, the operation of the tube 1 may not be affected.

The embodiments of Figs. 23 and 24 illustrate in their broad form, therefore,vthat all of the systems heretofore discussed and hereinafter treated are adaptable for modulating radio-frequency transmitters to transmit signals containing information concerning the forces acting upon the transducers of the present invention. Such circuits are particularly useful for telemetering, where movement of, for example, the transducer ring electrode, or variations of the impedance elements or other variable elements of the transducer circuits previously and hereinafter discussed, may be eifectedl in response to such forces as atmospheric pressure, wind velocity, temperature, humidity, and the like, as later more fully discussed. The information resulting from the action of these forces upon the transducer of the present invention may thus be received and detected at a remote station in the receiver, 163, Fig. 23.

Transducers operating under the control of such forces are illustrated in Figs. 25 to 30 and 47. The circuits of Figs. 25 and 26 illustrate changes in temperature effecting controlling influences upon the transducer of the present invention. In Fig. 25, the transducer 1 is shown energized from a generator 17 in the manner discussed in connection with the embodiment of Fig. 7. In place of the conventional condenser or other impedance element C1, however, two spaced electrodes 171 and 173 are shown coupling the principal electrode 3 to one side of the generator 17. From the same side of the generator 17 a balancing condenser C2 connects to the principal electrode 5. The other terminal of the generator 17 connects to the ring electrode 9, which, in this particular case, may be fixed. In between the spaced electrodes 171 and 173, is a temperature-indicating device such as, for example, a mercury-filled thermometer 175. As the mercury or other temperature responsive liquid in the thermometer rises and falls in response to temperature variations. therefore, more or less liquid is present between the electrodes 171 and 173, thereby changing the capacitance C1 and producing a corresponding direct-current signal in the output circuit 2-4, as before discussed.

In the embodiment of Fig. 26, a similar tube 1 is shown connected in the same type of circuit. The ring electrode 9 may be movable, however, in response to a bimetal relay or similar temperature-responsive strip 177. As the bi-metal relay or other device 177 bends in response to changes in temperature, it moves the ring electrode 9 to produce a corresponding direct-current voltage indication in, for example, the meter M in the output circuit 2-4.

As still another example of the type of control circuit that may operate upon the transducer of the present invention, a pressure or altitude device is indicated in Fig. 27. The previously discussed system of Fig. 45 may be used for this purpose also, outside pressure acting upon the bellows 11 in opposition to the gas pressure within the tube 1. The principal electrodes 3 and 5 of the gasdischarge tube 1 of the system of Fig. 27, however, are shown connected to spaced electrodes 181 and 133 that cooperate with a thin central conducting membrane or electrode 185, connected to one terminal of the generator 17. The other terminal of the generator connects with the ring electrode 9, which may, in this case, be fixed. The center electrode 185 serves as a common condenser plate for electrodes 181 and 183 and also divides a chamber into an upper portion 179 and a lower portion 187. The leads from the electrodes 3 and 5 are shown passing through sealed insulators in the right-hand walls of the upper and lower chamber portions 179 and 187. The upper chamber portion 179 is provided with an inlet or outlet 189, and the lower chamber 187 is provided with an inlet or outlet 191. If one of these chambers such as, for example, the chamber 187 is evacuated, and the corresponding inlet 191 is sealed, as is well-known in the art, then variations in atmospheric pressure resulting from the action of air passing through the inlet 189 into the upper chamber 179 and acting upon the member 185, will result in movement of the membrane member 185, resulting in direct-current indicating voltages in the output circuit 2-4. If a meter M, for example, is connected in the output circuit, variations in barometric pressure caused, for example, by altitude, may be indicated. We have, as another illustration, employed the circuit of Fig. 27 as a plesythmograph and have found that the pulsating blood pressure of a human finger inserted in, for example, the inlet 189 produced corresponding voltage indications in the meter M. With a tape recorder substituted for the meter, we have recorded the pressure cycle of the blood stream. As still another illustration, if a conventional Pitot tube is employed, as on an aircraft, with the in-rushing air stream fed to, for example, the inlet 189 and the quiescent air to the inlet 191, the velocity of the aircraft or of the air stream may be measured on the meter M.

Another type of device that may be employed to control the transducer of the present invention is illustrated in Fig. 28. A metallic or other conductive indicator, needle or arm 193 of a meter, clock, scale, counting device, or other registering device 195 is caused to rotate past the wire electrodes 3 and 5 of the transducer 1. The electrode 5 is energized from one terminal of, for example, the radio-frequency generator 17 and the needle or indicator 193 is connected to the other terminal to act in a similar fashion to the external movable ring electrodes previously discussed. Electrodes 3 and 5 are coupled by a capacitor C. In the output circuit 2-4, therefore, there will result adirect-current voltage each time the pointer 193 moves into the vicinity of the gas tube 1, producing assymmetry of iield strength. The circuit of Fig. 28 is thus adapted to producing counting voltage impulses or voltages that measure the position of the indicator 193.

Another force that may be measured in accordance with the present invention, as also discussed in the said copending application, is acceleration. A circuit is illustrated in Fig. 29 in which the gas tube or other transducer 1 is connected to a circuit of the type discussed in connection with the embodiment of Fig. 7.v The condensers Ci and C2, however, are operated in response to acceleration or other forces as will now be explained. The principal electrode 3 is connected through a lower and a relatively movable upper condenser plate of the condenser =Ci yto 1a conducting arm 197 that may be centrally `:pivoted about ashaft 199 that connects Atorrie terminalfofthe lso'urceor generator 17. The-otherprin:ipallelectrodeS l.is connected through lower .and 'relatively movable upper condenser plates ofthe-condenser C2 tothe `other end of the'arm :197. The varm 197 may be spring mounted, yas by springs 101, connected to a wall 103. yAs Vthe arm 197 pivots about the-shaft 199 in response to angular acceleration or other forces, the yupper condenser plates v4of 'the @condensers C1 and `Czare oppositely moved toward 'or away from ltheir respective lower condenser plates, thereby changing the relative magnitudes of condensers Ci and C2 and `accordingly varying the field strength yat the principal electrodes Stand`5. The result in the output circuit 2 4 is a directcurrent voltage lthat ymay be indicated, recorded, lor otherwise used for measurement or control as is -well -known in the art.

`As still another application of the present invention, reference-is made to the system of 30 `the `electrical connections 'of whichare substantially identical with those previouslysdiscussed in connection withthe systemof-Fig. 2'5. VThe spacede'lectrodes I17.1 and :173, however, are in this case shown opento Vproducea considerable strayeld ofradio-'requency energy. If an object175, for example, is ybrought within thisstrayiield, alvariation in capacitance between the electrodes `17.1 .and l173 will result, thereby producing variations in the `potential gradients within the tube 1 and a corresponding output direct-current voltage inthe output circuit 2 4. The arrangement of 'F.ig. V340 is thus .particularlysensitive for object-detection or counting, for dielectric measurements, vforthe inspection-of metallic particles in sealed packages, for mine detection, and Hlsimlar applications. It should also be mentioned that, should there be .provided between the electrodes 171 and 173 'of the systems, for example, of Figs. 25 and 30, hygroscopic material such as silica .gel which absorbs moisture rand thereby alters its dielectric constant, lthe output of the transducer will Agive information regarding the relative humidity 'of the atmosphere 'affecting the hygros'copic material. t i Q Still another application 'of 'the pre's'ent invention is illustrated in Fig. 47 in which the transducer 1 operates as a strain gauge or linear accelero'me'ter. vrlhe circuit is very similar'to that of Fig. 27, employing condenser 'plates 181 and 1:83 respectively connected to the principal electrodes :5 and 3 that cooperate with a 'common movable central electrode l185. The common electrode -185 may be moved up and down vin accordance with 'a weightjor other force y241 acting upon a member 243 that 'is 'spring mounted, as illustrated at 245, to a fixed meniber l247.

The voltage in the output circuit 2 4 will measure the weight or other forces acting upon the member -243 in opposition to the springs '245.l .A n v Again reference is made to the fact that the systems 'of Figs. 25 to 30, 45 'and 47, as well as the vother -embodiments of the invention, 'may be used in conjunction with radio transmitters, as 'illustrated in Figs. v23 `-and 2.4,.for telemetering 'measurements or other remote transmissions in 'order to permit the reception of voltage signals 'that measure particular forces, quantities or movements. Y

'In addition to `the facility Vof the transducer of 'the present invention Vin measuring "circuits,` the present invention provides 'also Va unique pick-'oit for producing voltages that maybe'fed to lerror circuits, including servomechanisms. In theembodiment of Fig. 31, as 'an illustration, three separate transducers 1, 12-1 Vand y141 are shown each connected in identical circuits of the "character previously discussed in connection with the 'embodiment of lFig. 7. The ringcl'ectrodes 9, 129 and 139 of the respective tubes 1, 121 and 141 V are shown connected 'to one terminal of 'each of three identical generators such as radio-frequency oscillators 17, all 'given the same reference number since they may, if desired 'be 'the same source. The other kterminals 'of the 'generators 17 are 4 connected 'through similar variable condensers Ci t and 'C2 to the respective principal electrodes o f the tubes, as before discussed. The output circuit 2 4 of each transducer is connected to a control amplifier lthat 'operates an :associated motor for regulating the angular position of some air-foil member, such as 'a rudder, an elevator, or an aileron of an aircraft or projectile. While `this embodiment is 4illustrated as applied 'to aircraft air-foil members, it is to be understood that 'it is of more general use l`being equally adapted `to control angular, linear or other movement 'of any desired member. The output circuit -2- 4 of the transducer 1 is shown connected to a control amplier that operates fa motor for regulating the Vposition of an Vaircraft rudder. The transducer 1-21 similarly produces voltages for controlling ythe position of elevators, while the transducer 141 operates through a `control amplifier and motor to regulate the adjustment of ailerons. Aircraft are customarily stabilized by means of well-known gyroscope-control circuits. These gyrosc'opes .produce lmovements which are customarily used to re-adjust rudders, elevators, and ailerons in vorder to stabilize the Hight of the aircraft. Such a conventional 'gyroscope system is illustrated at 105. It is more fully 'discussed hereinafter in connection with the systems of Figs. 40 to 43. l The condenser C1 of each of the transducer circuits is shown connected by a Adotted line 'to a corresponding portion of the gyroscope system to illustrate mechanical ganging thereto as later fully treated in the discussion of Figs. v4() to 43. The opposite condensers Cz of each transducer are each similarly shown mechanically ganged to the conventional corresponding pilots controls 107. As the pilot moves his rudder, elevator and aileron controls, he thus automatically correspo'ndingly varies the values of the responsive condensers C2. This results in unbalancing the potential gradients in the respective transducers 'and -producing corresponding direct-current voltages that, through the respective control amplifiers, -operate the respective motors to vary the position ofthe rudder, elevators and ailerons in response to the pilots settings on his controls 107. The aircraft thus varies its flight position in accordance with these adjustments. The gyroscope system 105, however, responds to the variations in ilight and, in so doing, correspondingly automatically varies the values of vthe respective condensers Ci in each transducer circuit. When the gyroscope position and the actual intended night position of the aircraftare in accord, the settings of the condensers C1 of leach vcircuit will correspond to -the settings vof the condensers C2, and no further correction voltage output will :result -from the transducers, the rudder, elevator and ailerons being vin their desired positions.

lStill yanother type of control circuit is illustrated in Fig. 32 in which the transducer 1 is provided with a variable capacitor C1 connected between the principal electrode 3 and one ofthe `terminals of the generator 17.

' The left-hand plate of this condenser C1 is shown movable toward or away from the right-hand plate in response to energizing voltages in an electromagnetic device 109. Extremely'small movements or displacements of the electromagnetic device 1'09 may produce in the transducer of the present invention appreciable voltage responses. The present invention, therefore, may be adapted to act -as an amplifier -of very small mechanical displacements. The output circuit 2 14'of the tube 1 is shown connected across, -for example, a meter M. A potentiometer, the slider of which is shown at 111, may be connected between the output vterminals 2 and 4 and may tap yoitpart of the output voltage appearing in the output circuit 2 4, in -orde'r to feed back to the coil or" the 'electromagnetic device 109. If, therefore, a small input voltage appears at the input circuit i12- 114 of the electromagnetic device 109, the left-hand plate of the condenser Ci will be moved a small amount in response thereto. Since no restoring force is present in this system, the lefthand condenser yplate lof 4the condenser zC1 will continue movement until it 'reaches its end position, or until the input voltage in the input-circuit 11'2 114 is interrupted, or until a voltage of opposite polarity is applied to the input circuit 112 114. Variations in the condenser Ci produced by this movement will also, as previously discussed, produce corresponding 'direct-current voltages in the output circuit 2 4 of the transducer '1, which, because of the sensitivity of vthe tubes of the present invention, may be many times larger than the original voltage -fed into the input circuit 112 114 of the electromagnetic device 109. This output voltage may be measured in any desired way as, for example, upon the meter M. As before mentioned, however, part of this output voltage is 'fed back by the potentiometer slider 111 to the input circuits 112 11l of the electromagnetic device 109 in opposite polarity to the original input voltage. When the feedback voltage has obtained a value equal to the original small input voltage tothe electromagnetic device, the electromagnetic system 109 will stop further movement, stopping further displacement of the left-hand condenser plate ofthe condenser Ci, and the meter M 

